Centrifuge for separating sludge from liquids



Filed May 4, 1953 O. A. V. KJELLGREN June 28, M955 CENTRIFUGE FOR SEPARATING SLUDGE FROM LIQUIDS United States Patent() l" CENTRIFUGE FOR SEPARATIN G SLUDGE FROM LIQUIDS Ove Allan Valentin Kjellgren, Stockholm, Sweden, as-

signor to Aktiebolag Separator, Stockholm, Sweden, a corporation of Sweden Application May 4, 1953, Serial No. 352,820

Claims priority, application Sweden May 14, 1952 8 Claims. (Cl. 233--7) This invention relates to the centrifugal separation of sludge from liquids, and has particular reference to an irnproved centrifuge for this purpose.

For separating sludge in the form of more or less solid particles from liquids, the centrifugal bowls or rotors used heretofore have in some instances been provided with an internal conveyor, such as a screw, for feeding the sludge mass to the sludge outlet in the centrifugal bowl. In cases where the sludge mass was to be freed as much as possible from the liquid in which the particles were sludged, the centrifugal bowl has been provided with a conical surface of revolution along part or all of its length, the conveyor screw being arranged to force the sludge along the conical surface inwardly toward the rotation axis of the bowl to a radius inside the liquid level formed during the separating operation, and the sludge mass being finally discharged over an edge in the wall of the centrifugal bowl. The sludge particles, which are heavier than the liquid, are forced inwardly and, so to speak, lifted out of the liquid against the action of the centrifugal force, because of the mechanical cooperation between the conveyor screw and the conical surface of the centrifugal bowl. Still exposed to the action of the centrifugal force, the retained liquid is then forced outward from the sludge mass and back to the liquid body outside the liquid level, so that the sludge mass is dehydrated more or less completely before being conveyed over the discharge edge and thereby thrown outward from the centrifugal rotor.

The degree of dehydration depends on the length of time during which the sludge mass, after being moved inside the liquid level (that is, out of the liquid body), is conveyed by the conveyor screw along the wall of the centrifugal bowl. However, it is not the liquid-expelling effect of the centrifugal force which is time-determined, but rather the mechanicalworking (the so-called kneading) to which the mass is subjected through cooperation between the conveyor and the conical surface. The longer this kneading is effected to work the sludge particle mass mechanically, the more complete is the removal of liquid therefrom. 4In order to have sutiicient time for drying to the required degree in a centrifugal rotor of the type described, it may be necessary to construct the centrifugal rotor with such a small cone angle of the conical surface, and therefore such a great length of the rotor, that the construction becomes impractical. Furthermore, such a centrifuge would have a small separating capacity.

According to the present invention, these inconveniences are removed by dividing the centrifugal rotor into two chambers separated from each other by partition means but connected in series, each chamber being provided with a conveyor, such as a conical screw, cooperating with an inwardly directed sludge path formed by a sloping surface or conical wall of the rotor. In addition to reducing the rotor length considerably and enabling a substantial increase in the separating capacity, this arrangement has the advantage that the sludge mass, after being freed in the first chamber from the main part of the liquid and discharged on a radius which is relatively Patented June 28, 1955 ICC small due to the conicity of the wall, is picked up in the second chamber by the second conveyor which operates on a considerably larger radius. Thus, the continuation of the dehydration in the second chamber is far more effective, since the second conveyor, being disposed on a considerably larger radius than the discharge from the first chamber, works the sludge mass While subjected to a considerably greater centrifugal force, which greatly accelerates and facilitates the dehydration.

For a better understanding of the invention, reference may be had to the accompanying drawing, in which the single illustration is a vertical sectional View of a preferred form of the centrifugal bowl or rotor.

In a centrifugal rotor 1 is a primary or first separating chamber 2 having at its peripheral portion a sludge space 3 surrounding the main separating zone, which may be provided with a conventional set of conical discs. Outside this separating Zone is a conveyor, shown as a screw 4, arranged to cooperate with the internal face of the cylindrical wall 5 of the rotor. The conveyor screw 4 extends inward along a conical wall 6 continuing from the wall 5. At its bottom, the screw is connected with a central portion 7 iixed on a shaft 8 which extends into a hollow shaft 9 supporting the bottom and outer wall S of the centrifugal rotor. The two shafts 8 and 9 are driven, as is customary in centrifuges of this type, at somewhat different angular speeds, so that there is a relative motion between them during operation. As a result, the conveyor 4 moves more or less slowly relative to walls 5 and 6 and in the direction to force the sludge mass in space 3 upward along wall 5 and inward along wall 6 toward the rotation axis. The Wall 6 terminates at its upper and inner portion in an overflow edge 10 forming a sludge outlet, which may be concentric with the rotation shaft. The sludge mass is forced over this edge by screw 4 and is then thrown out centrifugally through a channel 11 into another separating chamber 12 divided from the first chamber 2 lby the conical wall 6, which thus forms a partition means. Chamber 12 is provided with a second conveyor screw 13 which also is secured to the central portion 7 and rotates relative to the rotor housing at the same angular speed as the first screw 4. During continued dehydration, the sludge mass is fed by the conveyor screw 13 upwardly and inwardly along a conical wall 14 to a sludge outlet 15, through which the mass in dry condition is thrown out centrifugally from the rotor.

The liquid to be treated is introduced into the centrifugal rotor from above through a stationary central tube 16 extending downward into a receiving chamber 1'7 in the rotor. From this chamber the liquid is led outward through a system of circumferentially spaced channels 18 to an annular space 19 located outside the set of conical discs 20 occupying the main separating zone of chamber 2. 4An auxiliary liquid is also fed to chamber 2 through a channel 21 communicating with a second receiving chamber 22, the latter receiving the auxiliary liquid from a larger tube 23 concentric with tube 16 and connected to an inlet 24. The two liquids, introduced at opposite end portions of chamber 2, flow counter-currently through space 19. This arrangement is particularly suitable when it is desired to separate solid particles from a liquid and simultaneously to liberate the particles as completely as possible from adherent liquid by washing, as in separating bleaching-earth from oil. The bleaching-earth particles will accompany the oil through channel 18 into space 19, while an auxiliary liquid (e. g. water) enters the same space through channel 21, which opens into chamber 2 at a distance beyond channel 18. The water will form a layer in the outermost part of space 19 and also till up chamber 3 nearest the wall of the rotor, while the oil forms a layer inside the water layer and flows into the disc set 20. The bleaching-earth particles are separated between the discs 20 and are thereafter forced outward centrifugally through the oil layer into the water layer, where they are liberated from adherent oil by washing and gradually move close to the rotor wall in space 3. The oil flows upward through openings 25 in the discs into a channel 26 which forms an oil overflow outlet discharging at 27, the entrance 26 to outlet 27 being separated from the entrance to sludge outlet by the outwardly extending wall 21a of the rotor. The water mass in the outer part of space 19 discharges downwardly through a channel 28 to an overflow outlet or edge 29, from which it passes from the rotor by way of outlet 30. The overflow edge 29 is located radially somewhat outside the channel 26, so that there is an equilibrium between the oil mass and the water mass, and the boundary level between them will, during operation, be located in space 19 between the inlet mouth of channel 28 and the outer radius of the discs 20. The overflow edge or sludge outlet 1t) is disposed on a somewhat smaller radius than is the edge 29, in order that a water level may be formed close to, or just outside, the edge 10.

The second chamber 12 has at its bottom a residual liquid outlet 31 disposed on a somewhat smaller radius than the largest diameter of the corresponding conveyor screw 13, so that during operation a liquid level is maintained at the radius of the outlet 31. Outlet 31 leads via chamber 32 to an outlet 33 in the external wall of the rotor.

Instead of bleaching-earth sludged in oil, other sludgecontaining liquids can, of course, be treated, among which are those in which the liquid phase is not unitary but consists of a mixture of liquids of different specific gravities, for example, vegetable oils such as olive oil, or animal oils. In that case, the secondary liquid inlet 21--24 is not necessary and the whole liquid quantity can be supplied through inlet 16-18. Also when treating bleachingearth, it is possible to mix an auxiliary liquid (i. e. water) in the oil before the centrifugal treatment, and introduce the mixture through inlet 16-18. The invention, therefore, is not confined to the double liquid supply system.

If the liquid in which the particles are sludged consists of a liquid mixture, the separating chamber 2 and the disc set 20 are also used for separation of the two liquids, the heavier liquid component, together with the sludged particles, moving outwardly to the space 19 and the lighter liquid component moving inwardly to outlet --27. The sludge particles are separated from the heavier component in space 3 and transported by conveyor 4 in the manner described, while the heavier liquid component discharges from the centrifugal. rotor through outlet 28- 29'. Consequently, the effect is substantially the same as when the liquid phase is unitary, and difers only in that the liquid mixture is separated in the inset.

I claim:

l. ln a centrifuge for separating sludge from liquids and having a centrifugal rotor in which a mass of the sludge particles is conveyed out of the liquid bodyyin the rotor to liberate the mass from liquid, the combination with said rotor of partition means dividing the rotor into first and second separating chambers each having a sloping surface forming a sludge path inclined inward toward the rotation axis of the rotor, and each chamber also having a sludge outlet located at the inner portion of the correspending inclined path, the sludge outlet of the first chamber serially connecting the two chambers, and a sludge conveyor in each chamber coacting with the rotor to move the sludge inward along said path to the corresponding sludge outlet, the first chamber having an inlet for the sludge-containing liquid and an overflow outlet located close to said axis for discharging liquid freed from sludge, and the second chamber having a separated residual liquid outlet located at a substantially greater radius from the rotor axis than said liquid overflow outlet for the first chamber, whereby the sludge in the second chamber is subjected to drying on a relatively large surface free from the liquid body therein and under a heavy centrifugal force.

2. The combination according to claim l, comprising also aA set of spaced conical discs in the first chamber forming thin separating spaces.

3. The combination according to claim l, in which said residual liquid outlet from the second chamber is spaced from the axis a distance such as to maintain the liquid body in the second chamber at a level which immerses only the outermost portion of the corresponding conveyor, leaving the main part of the second chamberifreeof the liquid body.

4. The combination according to claim 1, in which said inlet for the sludge-containing liquid opens into one end portion of the first chamber, the first chamber also having an auxiliary liquid inlet opening into the opposite end portion of the first chamber in position to effect countercurrent tiow of the two liquids, whereby the sludge passing to said sludge outlet of the first chamber is washed.

5. In a centrifuge for separating sludge from liquids and having a centrifugal rotor in which a mass of the sludge particles is conveyed out of the liquid body in the rotor to liberate the mass from liquid, the combination with said rotor of partition means dividing the rotor into first and second separating chambers each having a sloping surface forming a sludge path inclining radially inward toward a sludge outlet from the chamber, the sludge outlet of the first chamber leading to the second chamber and thus serially connecting the chambers, and a sludge conveyor in each chamber coacting with the rotor to move the sludge inward along said path to the corresponding sludge outlet, the first chamber having an inlet for the sludge-containing liquid, and each chamber also having a liquid outlet determining the level of the liquid body in the chamber, said liquid level in the second chamber being located further outward along the corresponding inclined sludge path than is the liquid level in the first chamber, whereby the sludge in the second chamber is subjected to a more complete centrifugal drying action than is the sludge in the first chamber.

6. The combination according to claim l, in which the first chamber has a second liquid overflow outlet located at a greater radial distance from theaxis than said first overflow outlet, the rotor having a channel leading from the outer part of the first chamber to said second overflow outlet for discharging a heavier liquid component, said sludge outlet from the first chamber being located at a smaller radius from the axis than the residual liquid outlet of the second chamber.

7. The combination according to claim l, in which said overliow outlet and sludge outlet of the first chamber arc radially spaced in relation to each other and the axis, the rotor having an outwardly extending wall which separates the entrances to said overflow outlet and sludge outlet of the first chamber from each other.

8. The combination according to claim l, in which the first chamber has a second liquid overflow outlet located at a greater radial distance from the axis than said first overflow outlet, the rotor having a channel leading from the outer part of the first chamber to said second overflow outlet for maintaining the liquid body in the first chamber at a level adjacent said sludge outlet of the first chamber.

References Cited in the file of this patent UNITED STATES PATENTS 1,113,005 Hartmann Oct. 6, 1914 2,435,623 Forsberg Feb. 10, 1948 2,649,816 Kuster et al Aug. 25, 1953 

1. IN A CENTRIFUGE FOR SEPARATING SLUDGE FROM LIQUIDS AND HAVING A CENTRIFUGAL ROTOR IN WHICH A MASS OF THE SLUDGE PARTICLES IS CONVEYED OUT OF THE LIQUID BODY IN THE ROTOR TO LIBERATE THE MASS FROM LIQUID, THE COMBINATION WITH SAID ROTOR OF PARTITION MEANS DIVIDING THE ROTOR INTO FIRST AND SECOND SEPARATING CHAMBERS EACH HAVING A SLOPING SURFACE FORMING A SLUDGE PATH INCLINED INWARD TOWARD THE ROTATION AXIS OF THE ROTOR, AND EACH CHAMBER ALSO HAVING A SLUDGE OUTLET LOCATED AT THE INNER PORTION OF THE CORRESPONDING INCLINED PATH, THE SLUDGE OUTLET OF THE FIRST CHAMBER SERIALLY CONNECTING THE TWO CHAMBERS, AND A SLUDGE CONVEYOR IN EACH CHAMBER COACTING WITH THE ROTOR TO MOVE THE SLUDGE INWARD ALONG SAID PATH TO THE CORRESPONDING 